1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system and related communication device, and more particularly, to a communication device and method of handling a service in an unlicensed cell in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Network operators propose to offload network traffic of the LTE/LTE-A system to an unlicensed cell, to ease load of the network traffic. For example, the eNB may provide services to the UE via the unlicensed cell. However, resource in the unlicensed cell is not always available, and it is not easy for the eNB to allocate the resource in the unlicensed cell. The operations on the unlicensed cell are even more complicated, when the UE operates on both a licensed cell and the unlicensed cell (e.g., in the CA case). The resource scheduling for the licensed cell and the unlicensed cell is thus an important problem to be solved.
Correspondingly, hybrid automatic repeat request (HARQ) feedbacks should be transmitted in response to usage of the resource. It is still unknown how the HARQ feedbacks can be transmitted and received, when the UE operate on the licensed cell and the unlicensed cell. Thus, the transmission and reception of the HARQ feedback is also an important problem to be solved.